Walking forward is an excellent way to get where you're going provided that you're facing the way you want to go, there are no obstacles in your way, you have legs, your feet aren't tied together, you don't walk off a cliff...
The difference is that Toady has already coded the ability to walk. Toady tends to take a lot longer to code in new AI to figure out much more complex tasks, like "recognizing when you are burning to death in a fire", and has yet to code his AI to "recognize you are exerting yourself into a coma and your last 8 charge attacks didn't do any good anyway", resulting in the hilarious sight of creatures like elephants and trolls charging until they collapse from exhaustion.
In 0.40.24, I saw a giant olm, a toothless creature half the size of a troll eventually gum a troll to death in a battle that lasted about a year because the troll would repeatedly ram the olm until collapsing from exhaustion, while the olm ineffectually pawed with clawless limbs and tried to nibble the troll to death. (The troll eventually bled to death from an eye wound.)
The same really goes for how a GCS will only attack the head, rendering a dwarf unarmored but for a copper helmet invincible. Because that's what the AI tells it to do, that's what it does.
The list of basic conditions that seems so stupid and obvious? Those are not conditions the AI is capable of judging for itself right now, just the same as the AI wasn't capable of recognizing fire was bad for years, or that suicidal attacks are bad now. Programming AI it detailed, difficult, easily stymied by the slightest mistake, and time-consuming.
Compared to all these things, a judgement call as to whether running or turning into a plant is an
extremely nuanced decision, one that defies a direct, clear-cut answer. (Unless there is no reversal of a plant transformation, in which case the answer is "never use this unless you want to commit suicide" as a tantrum alternative or maybe a religious fanaticism from elves thing. And again, judging by Toady's other spells, there's zero guarantee that it's "game balanced" or "sane to use".)